[All] Fold env_texturetoggle inputs into CBaseEntity

[SirYodaJedi]

This deprecates env_texturetoggle, reducing entity spaghetti. Inputs have been renamed to avoid conflicts in existing maps, in case a entity has the same name as a env_texturetoggle.

FGD entries are as such, and can be added to the Targetname BaseClass:

	input	IncrementTextureFrameIndex(void) : "Increments entity's current texture frame by one."
	input	SetTextureFrameIndex(integer) : "Sets entity's texture frame to the specified index."

I doubt this works on sprite models and studio models, but there is no collective C++ class that all brush entities and info_overlay_accessor inherit that sprite and studio entities do not.